JPS6026790B2 - Process for producing phthalic anhydride from O-xylol or naphthalene - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an advantageous process for the preparation of phthalic anhydride by oxidizing o-xylol or naphthalene over a supported catalyst containing vanadine pentoxide and titanium dioxide.

As is known, phthalic anhydride is produced according to industrial methods by catalytic air oxidation of o-xylol or naphthalene in fixed bed tubular reactors.

Particularly suitable catalysts for this process are supported catalysts consisting of a spherical inert support and a catalytically active substance of vanadine pentoxide and titanium dioxide applied as a thin layer thereon. Catalysts of this type are known, for example, from German Patent No. 14
It is described in the specification of No. 4259. Also, a supported catalyst in which phosphorus is added to the catalyst material (German Patent Application Publication No. 1)
769998) is also already in use. This known method generally operates as follows.

A mixture of an oxygen-containing carrier gas, such as air, and the hydrocarbon to be oxidized is introduced into a number of tubes arranged in the reactor and in which the catalyst is present. To control the temperature, the tube is surrounded by molten salt, in which 350 to 420 qo
temperature is maintained. In this procedure, interfering formations are formed which are very difficult to separate from the desired phthalic anhydride and degrade the quality of the phthalic anhydride. In the production of phthalic acid from o-xylol, this is especially an aldehyde, such as phthalide, and especially naphthoquinone if naphthalene is used as starting material. The formation of this by-product increases as the loading of the air with hydrocarbons to be oxidized increases. However, for economical production, a high loading of air with the hydrocarbons to be oxidized is desirable. A high load is a load that exceeds the lower explosive limit of a mixture of air and hydrocarbons, e.g.
It means a load of 100 days. The formation of by-products can be suppressed, for example, by carrying out the oxidation at higher temperatures, lower gas volumes (longer residence times) or lower air hydrocarbon loads. However, in this case, the yield of phthalic anhydride and the amount of feed into the reactor are reduced. It has already been proposed to use catalysts whose catalytically active substances cause a reduction in side reactions by the addition of various additives.

But this did not bring the expected results. Either an overactive catalyst is obtained which only allows a lower loading of the air with hydrocarbons and gives a poorer yield;
Either the catalyst had too low an activity, so that although good yields were obtained, it was heavily contaminated by the forming organisms and thus produced phthalic anhydride of poor quality. It has therefore been an industrial challenge to find a process for the preparation of phthalic anhydride that makes it possible to obtain high yields and purity of the product at higher loadings of the carrier gas with hydrocarbons.

We found that the first 25 to 5 evacuation volume % of the catalyst volume in the direction of flow of the mixture from o-xylol or naphthalene and the carrier gas contains vanadium pentoxide and titanium dioxide in the active substance. It further contains 0.01 to 0.0% with respect to titanium dioxide. % by weight of rubidium but no phosphorus, and the remaining catalyst contains vanadium pentoxide and titanium dioxide as main components in the active material, and further contains 0.02 to 0.0% by weight of titanium dioxide. When the box contains % phosphorus by weight but no rubidium,
340-500 pm on a supported catalyst coated with a catalytically active material containing vanadium pentoxide and titanium dioxide as main components.
It has been found that particularly advantageous results are obtained in the production of phthalic anhydride by the catalytic oxidation of o-xylols and/or naphthalenes by conducting the o-xylols or naphthalenes together with an oxygen-containing carrier gas at a temperature of Ta.

According to the novel process, the catalytic oxidation of the hydrocarbons is carried out by means known per se, for example in a tubular reactor with salt bath cooling at a temperature of 340 DEG to 500 DEG C., preferably 350 DEG to 400 DEG C. 18-4 enemy diameter and 2-3.
A reactor tube having a length of 5 mm is filled with catalyst.

The catalyst is a supported catalyst, which consists of a catalytically inert support having a diameter of 3 to 13 ribs and a catalytic material applied thereon as a thin layer. The carrier is, for example, spherical or preferably circular. It consists of crystallized or fused silicates, ceramics, alumina, silicon carbide or quartz. The catalytically active material which coats the support with a layer thickness of 0.05 to 1 willow contains, for example, 1 to 3% by weight of vanadium pentoxide and 70 to 92% by weight of titanium dioxide. It can optionally also contain small amounts of antimony, zircon or tin, for example in the form of their oxides, for example up to 5% by weight, based on the catalyst material. The active material accounts for approximately 3-5% by weight of the finished supported catalyst. According to the invention, the first 25-5% by volume of the total volume of the catalyst in the direction of flow of the mixture from the hydrocarbon and oxygen-containing carrier gas
, preferably 30 to 4% by volume, in the active substance with respect to the titanium dioxide therein. A phosphorus-free catalyst containing round weight % rubidium, preferably 0.15 to 0.2 weight %, is charged.

The remaining catalyst is 0.02 to titanium dioxide in the active material.
~0. Mother weight %, preferably 0.05-0. Contains approximately 10% phosphorus by weight and no rubidium. The catalyst charge therefore consists of two layers: a rubidium-containing catalyst layer and a phosphorus-containing catalyst layer. However, the catalyst may be arranged such that the first catalyst layer containing rubidium but not containing phosphorus consists of two or more layers of catalyst, the rubidium content of which decreases from layer to layer in the direction of the flow of the reactant gas. You can also do it. Similarly, the phosphorus-containing catalyst layer may consist of two or more layers of catalyst, the amount of phosphorus increasing in the direction of flow. The catalyst layer may be present in one reactor or, for example, in two reactors arranged one after the other. What is decisive is only the spatial arrangement of the catalyst with respect to the direction of flow of the reactant gas. The tube has a length of, for example, 2 to 3.5 mm,
and if the process is carried out in a conventional tubular reactor through which the reaction gas flows from top to bottom in a known manner,
The tube is first filled with phosphorous-containing catalyst to a filling height of e.g. 0.99 to 2.24 skin and then topped with e.g.
．． The rubidium-containing catalyst is stacked at a packing height of 60 to 1.44 m. The height of the entire catalyst in the tube is approximately 1.
80 to 3.50, preferably 2.60 to 3.20. The preparation of supported catalysts takes place, for example, by applying the active substance to a support by means customary per se.

For example, operate as follows. Vanadium pentoxide or a vanadine compound that changes to vanadine pentoxide upon heating,
For example, ammonium vanadate or the oxalate, sulfate, acetate, tartrate or salicylate salt of vanadine may be dissolved in water or an organic solvent such as formamide, diethylacetamide, ammonium rhodanide, molten urea or an alkali as appropriate. Mixing with finely divided titanium dioxide with the addition of rubidium compounds or scale compounds, and the mixture often having a mushy density, for example in a coating drum,
Spray onto a carrier heated to 100 to 45,000 ℃. Finely divided titanium dioxide is obtained, for example, by grinding, particularly preferably by grinding in a colloid mill. Suitable rubidium compounds are, for example, rubidium sulphate, rubidium carbonate, rubidium acetate or rubidium nitrate.

With the exception of rubidium sulfate, these compounds convert to oxides at relatively high temperatures. In the catalyst, rubidium is present as rubidium oxide, rubidium sulfate or rubidium vanadate. Suitable phosphorus compounds are, for example, ammonium phosphate, phosphoric acid, phosphorous acid or phosphoric acid esters.
Titanium dioxide is preferably used in the anatase form, which advantageously has an internal surface area of from 3 to 100 w/h, particularly preferably from 7 to 50 w/h, and below 1 f/h
For example, it shows a particle size of 0.4 to 0.8 degrees. According to the new process, phthalic anhydride is obtained in good quality and high yield.

A particular and unexpected advantage is that high yields and qualities are obtained even at relatively high o-xylol or naphthalene loadings of air, e.g. ~8
This results from the fact that it is also obtained at a loading of o-xylol or naphthalene of 0. Example 1 [a} Production of catalyst 1 600 steatite rings with an outer diameter of 8 skin, a length of 6 sides and a wall thickness of 1.5 sides were heated to 260 qo in a coating drum,
and anatase with an internal surface area of 11/40
0 night, vanadyl oxalate (vanadium content corresponds to V2Q41%) 73.2 night, water 500 night, formamide 10
Spraying a suspension consisting of 1.0% of rubidium carbonate and 1.09% of rubidium carbonate such that the weight of the applied catalytic material is 10% of the total weight of the catalyst.
Make it so that

The catalytically active material applied in this way was 0.2 rubidium oxide.
02% by weight (equivalent to 0.18% by weight of rubidium)
, 7.0% by weight of vanadium pentoxide and 92% of titanium dioxide.
It consists of 84% by weight, of which there is 35.3 atoms of vanadium and 1 atom of rubudium. The rubidium content is 0.2% by weight relative to anatase. 'b} Manufacture of catalyst {a} Proceed as in {a} except that 4.87 g of ammonium hydrogen phosphate is added instead of rubidium carbonate.

In the finished catalyst, the weight of the applied material amounts to 10% by weight of the total weight of the catalyst. The catalyst layer contains 0.3% by weight of phosphorus and 7.5% of vanadium pentoxide. weight percent of titanium dioxide and 92. % by weight. The amount of phosphorus is 0.32% relative to anatase. {c) 1.60 of oxidation catalyst 0, followed by 1.20 of catalyst 1, 2
A 3.25 mm long iron tube with an internal diameter of 5 mm is charged.

This tube is surrounded by molten salt for temperature regulation.
4. hourly through the tube from top to bottom. 97% o air in arc
- Xylol leads at a load of about 60 m/N or less. At this time, the results are shown in the following table (the yield is 10% of the obtained phthalic anhydride).
0% of o-oxylol or naphthalene (in % by weight) is obtained. Comparative Experiment Using only the catalyst at a bed height of 2.80 and carrying out the oxidation at 37,530 and 37.5 o-oxyl loads, phthalic anhydride was obtained in a yield of 10% by weight; This shows a phthalide content of less than 0.001%.

In this case, an o-oxyl loading of more than 42% results in damage to the catalyst due to the high local temperatures that occur in this case. Using only catalyst 1 containing rubidium, the results shown in the following table are obtained. Example 2 The procedure is as in Example 1, but naphthalene is oxidized instead of o-xylol.

The amount of air passed through the catalyst tubes per hour is moderate, and the air load due to naphthalene is less than 60/N.
The naphthalene used has a naphthalene content of 99.1% and a sulfur content of 0.4%. The results shown in the following table are obtained. Using rubidium-containing catalyst 1 alone at a bed height of 2.80, phthalic anhydride is obtained in a yield of 102% by weight, but the amount of naphthoquinone is 2.3%.

Claims (1)

Claims: 1. The first 25 to 5 volumes of the catalyst in the direction of flow of the mixture from o-xylol or naphthalene and the carrier gas.
0% by volume of the catalyst contains vanadium pentoxide and titanium dioxide as main components in the active substance and further contains 0.01-0.3% by weight of rubidium relative to titanium dioxide but no phosphorus; and the remaining catalyst contains vanadium pentoxide and titanium dioxide as main components in the active substance,
Furthermore, a supported catalyst coated with a catalytically active substance containing vanadine pentoxide and titanium dioxide as main components, characterized in that it contains 0.02 to 0.8% by weight of phosphorus based on titanium dioxide but does not contain rubidium. Above, 340-500℃
A process for the preparation of phthalic anhydride by catalytic oxidation of o-xylol and/or naphthalene by conducting the o-xylol and/or naphthalene together with an oxygen-containing carrier gas at a temperature of . 2. Phosphorus-free catalyst accounts for the first 30-45% by volume of the catalyst volume.
2. Process according to claim 1, characterized in that the rubidium-free catalyst forms the remaining catalyst volume. 3. Phosphorous-free catalyst is present in the active material with zero concentration of titanium dioxide.
．． Claims containing 15 to 0.22% by weight of rubidium and characterized in that the rubidium-free catalyst contains in the active substance 0.05 to 0.6% by weight of phosphorus relative to titanium dioxide The method described in item 1 of the scope. 4. Process according to claim 1, characterized in that the mixture of carrier gas and o-xylol or naphthalene has a hydrocarbon content of 44 to 100 g/m^3.